Multiple sclerosis (MS) is the most prevalent, demyelinating disease of the central nervous system (CNS), causing progressive physical and cognitive disability. MS is considered an autoimmune disease, as supported by the presence of activated myelin basic protein (MBP)-specific T cells. To study the immunological abnormalities of MS, the Racke laboratory has compiled an extensive collection of peripheral blood mononuclear cells (PBMC) from healthy subjects (n=15) and MS patients (n=60). We propose to use this collection to define the miRNA profile of T lymphocytes from healthy and MS patients. miRNAs are small non-coding RNAs that regulate important developmental, differentiation and disease processes, but their role in MS remains unexplored. We hypothesize that miRNA dysregulation causes the T cell defects that underlie MS pathogenesis. Specific Aim 1. Identification of the miRNA signature of Multiple Sclerosis naive CD4 T cells. This aim will test the hypothesis that naive CD4 T cells from MS patients have a baseline dysregulation of miRNA expression, perhaps making them more susceptible to self-reactive immune responses. Unstimulated naive CD4 T cells from i) healthy, ii) treatment-naive relapsing-remitting multiple sclerosis (RRMS), and iii) treatment-naive primary progressive MS (PPMS)subjects will be sorted from whole blood PBMC prior to RNA isolation. miRNAs will be detected by a comprehensive multiplexed real-time PCR assay and targets will be identified. Specific Aim 2. Identification of the miRNA signature of Multiple Sclerosis activated memory CD4 T cells. This aim will test the hypothesis that, prior to and following activation, the memory CD4 T cell miRNA profile varies between healthy and MS patients. Samples will include resting and phorbol myristate acetate (PMA)/Ionomycin-activated PBMC from i) healthy, ii) treatment-naive RRMS, and iii) treatment-naive PPMS subjects. Memory CD4 T cells from these samples will be sorted prior to activation, RNA isolation and miRNA analysis, as described in Specific Aim 1. These studies will define the miRNA profile of MS patient memory T cells and the changes associated with activation. This initial analysis of miRNA in naive and memory CD4+ T cells will allow us to determine if altered miRNA expression in MS patients influences the development of encephalitogenic T cells that mediate MS pathogenesis and identify potential MS biomarkers. Comparison of naive, memory and activated T cells will determine at which stage of T cell maturation miRNAs may influence T cell function in MS. Although this initial study will focus on treatment-naive patients, we have PBMC cells from multiple time points from most patients, many of whom began an immunomodulatory therapy. Therefore, this data will provide a foundation for evaluating the effects of specific immunomodulatory therapies on normalizing miRNA levels that may be associated with therapy responsiveness. PUBLIC HEALTH RELEVANCE: Multiple Sclerosis (MS) is an immune-mediated disease that destroys the myelin sheath around axons, resulting in impaired nerve conduction and functional loss. Since the cause of MS is unknown, there is no cure, and current therapies are only partially affective, approximately 350,000 Americans live with MS and many will become physically handicapped during their lifetime. The current study uses a new approach to understanding the mechanism by which immune cells which are designed to protect self, actually damage self in MS. This study is designed to identify normally occurring microRNA that may be dysregulating, promoting autoimmunity. The data will enable us to identify new therapeutic targets and disease biomarkers for MS.